Au Cluster-derived Electrocatalysts for CO2 Reduction

Abstract

Metal clusters often exhibit superior chemical, electronic, and geometrical properties and can show exciting catalytic performance. The catalytic behaviour of the clusters is strongly affected by their size and composition, offering unique opportunities to fine-tune such materials for a specific application. In this study, atomically precise [Au₆(dppp)₄](NO₃)₂, [Au₉(PPh₃)₈](NO₃)₃, [Au₁₃(dppe)₅Cl₂]Cl₃ and Au₁₀₁(PPPh₃)₂₁Cl₅ clusters were synthesised, characterised and their activity for electrocatalytic CO₂ reduction is compared. These Au clusters were deposited onto carbon paper to serve as the cathode for the electrochemical reduction of CO₂. The experimental studies suggest that the clusters remain intact upon deposition on the carbon paper but undergo agglomeration during CO₂ electrolysis. The cluster-based catalysts demonstrated high selectivity (75%—90%) for CO production over hydrogen evolution reaction. Upon calcination, the activity of the cluster-based electrodes decreases, which can be attributed to the agglomeration of small clusters into larger bulk-like nanoparticles, as suggested by XPS, XAS and SEM.

Graphical Abstract

A series of phosphine-protected gold clusters supported on carbon paper were studied as CO₂RR electrocatalysts. The CO₂RR activity was dependent on their size and ligand density. Thermal annealing of the catalysts invariably lowered CO selectivity due to agglomeration of the clusters into larger nanoparticles.